1. Field of the Invention
The present invention relates to an optical recording medium including a phase change type recording layer and a method for testing that optical recording medium.
2. Description of the Related Art
Conventionally, an optical recording medium including a plurality of information layers on a substrate is widely known, in which at least one information layer other than the farthest information layer from a light-incident surface on which a laser beam is incident is translucent and includes a recording layer formed of a phase change material (see Japanese Patent Laid-Open Publication No. 2003-22572, for example).
In that optical recording medium, the laser beam passes through the information layers when recording or reproduction of data is performed for the farthest information layer from the light-incident surface. Thus, the information layers should be highly transparent with respect to the laser beam and it is necessary to form the recording layer and a reflective layer in the information layer to be thin.
However, a case is considered where data is recorded on the thin recording layer formed of a phase change material, the optical recording medium including that recording layer is then stored at a high temperature for a long time (for example, at 80° C. for 24 hours), and thereafter data is overwritten once in a portion where data is recorded before the storage. In this case, a jitter value of a reproduction signal is largely degraded.
That problem becomes more pronounced as a recording rate is larger or the thickness of the recording layer is thinner. Thus, that problem prevents increase of the recording rate in the optical recording medium and increase of recording density of the optical recording medium by increasing the number of the information layers.